Polysubstituted piperazinones ("PSP" for brevity) are well known stabilizers for synthetic resinous materials exposed to environmental degradation and ultraviolet (uv) light, in particular. Such materials are disclosed in U.S. Pat. Nos. 4,167,512; 4,190,571; 4,240,961; 4,292,240; 4,297,497; 4,466,915; and 4,480,092, inter alia. The commercial process for the manufacture of the PSPs is by the non-catalytic base-induced ketoform synthesis described in U.S. Pat. No. 4,466,915 patent, the disclosure of which is incorporated by reference thereto as if fully set forth herein.
This invention derives from the discovery that particular 1-(alkylamino)alkyl-PSPs having 2 or 3 (CH.sub.2) groups connecting the N.sup.1 of the diazacycloalkane ring to the N atom of the terminal amine group, are peculiarly prone to decomposition of subjected to elevated temperatures in the range in which the ketone (from which the PSP is derived) boils, hence termed "water-sensitive". This water-sensitivity is particularly evident when such PSPs are contacted with large amounts of water. Therefore the invention relates to the recovery by distillation of a PSP from an essentially anhydrous reaction mass without using water in any step during synthesis of, or, recovery of the product.
U.S. Pat. No. 4,299,497 reference states "The preferred alkali is an aqueous alkali metal hydroxide solution such as aqueous sodium hydroxide, or potassium hydroxide, preferably in the range from about 20 percent to 70 percent solutions. If the alkali metal hydroxide is used in solid form, it is preferably in finely divided form typically less than 80 U.S. Standard mesh in size. The amount used is not critical but at least a trace amount appears to be essential for the progress of the desired reaction. It is preferred to use sufficient aqueous alkali solution to form a visually distinct aqueous phase in the presence of the organic solvent phase. In general, the amount of aqueous alkali used is preferably at least 5 percent by weight of the reaction mass. There is no advantage to using more aqueous alkali than about 75 percent by weight of the reaction mass." (col 11, lines 33-48).
The synthesis was illustrated in U.S. Pat. No. 4,297,497 in examples which required the addition of a phase transfer catalyst (BTAC) because at the time, that was the only way to run the reaction. Specifically, with respect to addition of the alkali, I stated in example 3 ".. 40 ml conc NaOH (50 % by wt) is dripped into the flask over about 30 mins. The reaction is allowed to proceed for about 5 hr.." (see col 13, lines 14-16). In another example (6) Lai stated "Then add 40 l conc NaOH (50 % by wt) to the reaction mixture dropwise, so the temperature does not exceed 30.degree. C." (see col 14, lines 23-26). The slow addition of NaOH is necessary because it is the exotherm-controlling step. Addition of the alkali in solid, finely divided particulate form, allowed better control of the rate of reaction. Because it was a phase transfer catalyzed reaction, one could add a large excess of alkali without adverse side effects, namely production of undesirable byproducts of side reactions. The addition of a very large excess of alkali in a non-catalytic synthesis, is in a different reaction environment, distinguishable because of the absence of the phase transfer catalyst, and is the nexus of the conventional (original) commercialization of the non-catalytic synthesis, and the present invention.
Briefly, the ketoform synthesis comprises reacting a N,N'-alkyl substituted ethylene diamine with an acyclic or cyclic ketone, and chloroform, in the presence of aqueous or solid alkali, and, a large excess of ketone, in the presence of a phase transfer catalyst, as described in the 4,167,512 patent issued Sept. 11, 1979, more fully in U.S. Pat. No. 4,297,497 pat. issued Oct. 27, 1981, the disclosures closures of which are incorporated by reference thereto as if fully set forth herein. Three years later, Lai described how to run the reaction without a catalyst in U.S. Pat. No. 4,466,915 pat., issued Aug. 21, 1984; and, about the same time how to use solid NaOH in a solvent (say, toluene) to function as an HCl acceptor to couple one or more PSP moieties to a triazine nucleus (by reaction of cyanuric chloride with the PSP) in U.S. Pat. No. 4,480,092, issued Oct. 30, 1984. U.S. Pat. No. 4,466,915 titled "Non-Catalytic Ketoform Synthesis" provides all relevant facts known about the prior art process as they relate to its commercialization in a conventional non-catalytic ketoform synthesis.
The ketoform reaction which generates the PSP by cyclizing the N,N'-alkyl substituted ethylene (or propylene) diamine, depends upon the generation of a CCl.sub.3 anion provided by the action of NaOH on chloroform. This aniongenerating function of the NaOH is provided by aqueous or solid alkali, in the presence of the phase transfer catalyst, and also when there is no catalyst present. In the reaction which uses solid NaOH to couple the PSP formed by the ketoform reaction with a triazine, the NaOH performs the function of a Hcl acceptor, allowing the PSP is displaced. The formation of HCl is unrelated to the formation of any ion. Both these reactions are taught in U.S. Pat. No. 4,480,092. In all illustrative examples which teach the formations of the PSP, aqueous sodium hydroxide was used because U.S. Pat. No. 4,480,092 referred to U.S. Pat. No. 4,167,512 (see col 11, line 43) which was the catalytic synthesis. No mention is made about the effect of a large excess of solid NaOH is the PSP synthesis because of the particular amount of the excess was not deemed critical. U.S. Pat. No. 4,167,512 patent taught a range from 5 percent to 75 percent by weight of the reaction mass (see btm of col 10).
On the other hand, U.S. Pat. No. 4,466,915 patent which deals with the non-catalytic synthesis, clearly spelled out the criticality of the excess of alkali (whether aqueous or not). It states "It is preferred to use sufficient aqueous alkali solution to form a visually distinct aqueous phase in the presence of the organic solvent phase. In general, the amount of aqueous alkali used is preferably about three (3) equivalents of the amine. A slight excess over three equivalent (sic) is preferable, but a large excess is to be avoided.
Through aqueous alkali is most preferable, water is not an essential requirement for the progress of the synthesis, though it will be appreciated that even where solid alkali metal hydroxide is used, there may be a trace of water associated with it." (see col 4, lines 53-63).
In all the references relating to the recovery of PSPs we used a water-imiscible chlorocarbon such as chloroform or methylene chloride in which most PSPs are preferentially soluble relative to their solubility in a ketone, to extract the PSP from the reaction mass. Since many of the PSPs formed were not substantially soluble in the ketone used as a reactant, were not known to be sensitive to being contacted with copious quantities of water, and were partly precipitated with the salt (NaCl, if NaOH was used), extraction with the chlorocarbon was a most convenient and effective way of extracting the PSP from the reaction mass. However since much of the ketone and some of the salt was extracted in the chlorocarbon, we used water to wash out the remaining ketone, and also the salt formed during the ketoform reaction. Since these references were to 1,4-PSPs in general, the sensitivity of PSPs with the 2 or 3 methylene group linkage, to water, was not known, and therefore never a consideration.
It was in the framework of the foregoing facts that we happened to find that a large excess of alkali, at least five moles for each mole of amine reactant used to produce the desired water-sensitive PSP, in a large excess of essentially anhydrous ketone, sufficient to completely dissolve the PSP formed, avoided the use of a chlorocarbon solvent and a water wash. Because this PSP was never contacted with water, this method desensitized the PSP's proclivity to degradation during the distillation steps required for its workup and recovery.